Coatings for relatively movable surfaces

ABSTRACT

A device has a microelectromechanical system (MEMS) component with at least one surface and a coating disposed on at least a portion of the surface. The coating has a compound of the formula M(CnF2n+1Or), wherein M is a polar head group and wherein n≧2r. The value of n may range from 2 to about 20, and the value of r may range from 1 to about 10. The value of n plus r may range from 3 to about 30, and a ratio of n:r may have a value of about 2:1 to about 20:1.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/333,829, filed Jul. 17, 2014, which is a is a divisional of U.S.patent application Ser. No. 13/784,423, filed on Mar. 4, 2013, U.S. Pat.No. 8,803,296, which claims priority to and the benefit of U.S.Provisional Patent Application Ser. No. 61/738,927, filed on Dec. 18,2012, entitled “Coatings for Relatively Movable Surfaces,” by W.Morrison, et al., both of which are incorporated herein by reference intheir entirety for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

REFERENCE TO A MICROFICHE APPENDIX

Not applicable.

BACKGROUND

Microelectromechanical system (MEMS) devices such as actuators,switches, motors, sensors, variable capacitors, spatial light modulators(SLMs) and similar microelectronic devices can have movable elements.For example, a typical SLM device comprises an array of movable elementsin the form of individually addressable light modulator elements whoserespective “on” or “off” positions are set in response to input data toeither pass or block transmission or reflectance of light directed atthe array from an illumination source. In the case of an SLM device usedin an image projection system, the input data corresponds to bits of bitframes generated from pixel hue and intensity information data of animage frame of an image input signal. The bit frames may be compilationsof bits in a pulse-width modulation scheme that utilizes weighted timesegment “on” or “off” periods for generation of corresponding pixel hueand intensity by eye integration during a given available image framedisplay period. A representative example of an SLM device includes adigital micromirror device (DMD), such as a Texas Instruments DLP™micromirror array device. DLP™ devices have been employed widelycommercially including in televisions, cinemagraphic projection systems,business-related projectors, and picoprojectors.

The mechanical performance of the moving elements within a MEMS devicecan be compromised by unintended adhesion. This type of adhesion can bereduced by coating contacting elements of the MEMS device with a coatingsuch as a passivating agent or lubricant. The coating can be added toaddress several problems with device operation. One such problem isstatic friction (stiction). Another problem can include dynamicfriction, which arises from the contact of moving elements in thedevice. Effective coatings can aid in reducing stiction and dynamicfriction by reducing the surface energy of the device. For rotatingdevices (such as a micromirror supported for rotation on a hinge in aDMD), repeated movement displaces molecules and permanently biases thezero state of the rotation. Passivation layers may reduce this hingememory accumulation by stabilizing certain states of the surface.

SUMMARY

In an embodiment, a device comprises a MEMS component comprising atleast one surface and a coating disposed on at least a portion of thesurface. The coating comprises a compound of the formulaM(C_(n)F_(2n+1)O_(r)), wherein M comprises a polar head group, andwherein n≧2r. The polar head group may comprise a central atom having acoordination number of 3, 4, or 5, at least one oxygen atom bound to thecentral atom, and/or a hydroxyl functional group bound to the centralatom. The polar head group may comprise at least one functional groupselected from the group consisting of: a carboxylic acid functionalgroup; a sulfonic acid functional group, a phosphonic acid functionalgroup, an amide functional group, and a hydroxamide functional group.The value of n may range from 2 to about 20, and the value of r mayrange from 1 to about 10. The value of n+r may range from 3 to about 30,and a ratio of n:r may have a value of about 2:1 to about 20:1. The MEMScomponent may comprise a digital micromirror device. The MEMS componentmay comprise at least one of an actuator, a motor, an RF switch, asensor, a variable capacitor, an optical modulator, a microgear, anaccelerometer, a transducer, a fluid nozzle, a gyroscope, or anycombination thereof. The coating may be disposed on the at least theportion of the surface as a self-assembling monolayer. A polydispersityof the compound may be less than about 2.0. The compound may comprise atleast one material selected from the group consisting of: aperfluoropoly(alkylene) monoether carboxylic acid, a perfluoro(alkylene)monoether sulfonic acid, a perfluoro(alkylene) monoether phosphonicacid, a perfluoro(alkylene) monoether carboxamide, and aperfluoro(alkylene) monoether hydroxamide, a perfluoropoly(alkylene)polyether carboxylic acid, a perfluoro(alkylene)polyether sulfonic acid,a perfluoro(alkylene)polyether phosphonic acid, aperfluoro(alkylene)polyether carboxamide, and aperfluoro(alkylene)polyether hydroxamide. The compound may comprise atleast one material selected from the group consisting of:perfluoro-3-oxadecanoic acid, perfluoro-2-oxaoctane-sulfonic acid,perfluoro-2-oxaoctane-phosphonic acid,N-hydroxy-perfluoro-2-oxaoctanamide, perfluoro-4-oxaheptanoic acid,perfluoro-4-oxaoctanoic acid, perfluoro-4-oxanonanoic acid,perfluoro-4-oxadecanoic acid, perfluoro-3-oxaundecanoic acid,perfluoro-3,6-dioxadodecanoic acid, perfluoro-3,6,9-trioxatridecanoicacid, and perfluoro-3,6,9,12-tetraoxatetrdecanoic acid.

In an embodiment, a device comprises a MEMS component or semiconductorcomponent comprising at least one surface and a coating disposed on thesurface. The coating comprises a compound comprising a hydrophilic headgroup bound to a hydrophobic tail, and the hydrophobic tail comprises afluorinated carbon chain and at least one ether functional groupdisposed within the fluorinated carbon chain. The hydrophobic tail maycomprise 1 to 10 ether functional groups disposed within the fluorinatedcarbon chain, 2 to 20 carbon atoms, and/or 3-30 total backbone atoms inthe fluorinated carbon chain. The hydrophobic tail may comprise aplurality of ether functional groups disposed within the fluorinatedcarbon chain, and/or a number of carbon atoms in the fluorinated carbonchain separating sequential ether groups may range from 1-6 carbonatoms. The fluorinated carbon chain may comprise a perfluorinated carbonchain. The coating may form a monolayer on the surface. The hydrophilichead group may be configured to have a chemisorption interaction withthe at least one surface. The MEMS component may be configured to moverelative to one or more surrounding structures.

In an embodiment, a method of protecting a device comprises receiving aMEMS component or semiconductor component, and disposing a coating on atleast one surface of the MEMS component or semiconductor component. Thecoating comprises an amphiphilic compound comprising a hydrophilic headgroup bound to a hydrophobic tail, and the hydrophobic tail comprises afluorinated carbon chain and at least one ether functional groupdisposed within the fluorinated carbon chain. The amphiphilic compoundmay comprise a compound of the formula M(C_(n)F_(2n+1)O_(r)), where M isthe hydrophilic head group, (C_(n)F_(2n+1)O_(r)) is the hydrophobictail, and where n≧2r. The hydrophobic tail may comprise 1 to 10 etherfunctional groups disposed within the fluorinated carbon chain, and/or 2to 20 carbon atoms. The hydrophobic tail may comprise a plurality ofether functional groups disposed within the fluorinated carbon chain,and a number of carbon atoms in the fluorinated carbon chain separatingsequential ether groups ranges from 1-6 carbon atoms. The fluorinatedcarbon chain may comprise a perfluorinated carbon chain. Disposing thecoating may comprise performing a vapor deposition process. The methodmay also include forming a monolayer on the at least one surface. Themethod may further include enclosing the MEMS component or semiconductorcomponent within a package after disposing the coating on the at leastone surface. The method may still further include reducing a surfaceenergy of the at least one surface relative to an uncoated surface usingthe coating.

These and other features will be more clearly understood from thefollowing detailed description taken in conjunction with theaccompanying drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and theadvantages thereof, reference is now made to the following briefdescription, taken in connection with the accompanying drawings anddetailed description:

FIG. 1 is a schematic illustration of an embodiment of a coatingcompound.

FIG. 2 is a schematic illustration of several embodiments of coatingcompounds having different polar head groups.

FIG. 3 is a schematic illustration of several embodiments of coatingcompounds having different hydrophobic tail section lengths.

FIG. 4 is a schematic illustration of several embodiments of coatingcompounds having different numbers of ether functional groups in thehydrophobic tail section.

FIG. 5 is a schematic illustration of an embodiment of a coating on asurface.

FIG. 6 is a flowchart of a method disposing a coating compound on asurface according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the drawings and description that follow, like parts are typicallymarked throughout the specification and drawings with the same referencenumerals, respectively. The drawing figures are not necessarily toscale. Certain features of the invention may be shown exaggerated inscale or in somewhat schematic form and some details of conventionalelements may not be shown in the interest of clarity and conciseness.Specific embodiments are described in detail and are shown in thedrawings, with the understanding that the present disclosure is to beconsidered an exemplification of the principles of the invention, and isnot intended to limit the invention to that illustrated and describedherein. It is to be fully recognized that the different teachings of theembodiments discussed infra may be employed separately or in anysuitable combination to produce desired results.

In the following discussion and in the claims, the terms “including” and“comprising” are used in an open-ended fashion, and thus should beinterpreted to mean “including, but not limited to . . . ”. The variouscharacteristics mentioned above, as well as other features andcharacteristics described in more detail below, will be readily apparentto those skilled in the art with the aid of this disclosure upon readingthe following detailed description of the embodiments, and by referringto the accompanying drawings.

On a micrometer or smaller scale, atomic level and microscopic levelforces between surfaces in contact become significant. Problems relatedto these types of forces are accordingly relevant to micromechanicaldevices, such as microelectromechanical system (MEMS) andnanoelectromechanical system (NEMS) devices. In particular, “stiction”forces created between moving parts that contact each other, eitherintentionally or accidentally, during operation can be a problem withmicromechanical devices. Stiction-type failures occur when theinterfacial attraction forces created between moving parts that comeinto contact with one another exceed restoring forces. Stiction cancause surfaces of these parts to either permanently or temporarilyadhere to each other, causing device failure and/or malfunction.Stiction forces are complex surface phenomena that generally includecapillary forces, van der Waals forces, and electrostatic attractionforces. As used herein, the term “contact” refers generally to anyinteraction between two surfaces and is not limited to the actualphysical touching of the surfaces. Typical micromechanical devicesand/or devices comprising semiconductor components can include, but arenot limited to, RF switches, optical modulators, microgears,accelerometers, worm gears, transducers, fluid nozzles, gyroscopes, andother similar devices or actuators. It should be noted that the term“MEMS” device or component is used hereafter to generally describe amicromechanical device, and includes both MEMS and NEMS devices.

MEMS and/or semiconductor components, which can experience repeatedphysical contact between moving parts, may utilize a coating compoundfor lubrication to reduce or prevent stiction and/or dynamic friction.Various elements in these devices often interact with each other duringoperation at frequencies between a few hertz (Hz) and a few gigahertz(GHz). Without adding some form of lubrication to these types of devicesto reduce stiction and wear between component surfaces, productlifetimes may range from only a few contacts to a few thousand contacts,which is generally well below a commercially viable lifetime.

Lubrication to reduce the stiction within operating MEMS devices may beachieved through the use of one or more chemical coatings on elementsurfaces. Many types of coating compounds such as alcohols, siloxanesand perfluorinated alkanoic acids can be used as MEMS device lubricants.The vapor phase deposition of the coating compound may result in aself-assembling monolayer (SAM) or similar ultra-thin layer of thelubricant growing over the surface of the element, thus preventing itsfunctional elements from making direct contact and permanently adheringto each other through surface energy effects/forces. For example, theDMD SLM has in some embodiments benefited from the use of saturatedperfluorinated carboxylic acids as a lubricant, including those havingcarbon chains lengths of C₈ and longer. However, the use of thesaturated perfluorinated carboxylic acids can be chemically incompatiblewith portions of a MEMS device. The saturated perfluorinated carboxylicacids may only be suitable within limited operating ranges, therebylimiting the operating conditions of the device.

Disclosed herein is a coating compound for use with a MEMS device or asemiconductor device. The coating compound may provide lubrication,passivation, and/or surface protection for one or more surfaces of theMEMS device and/or a semiconductor device. The coating may generallycomprise a tail having one or more ether groups interspersed along acarbon chain. Such a configuration may improve the compatibility of thecoating with the components of the MEMS and extend acceptableperformance of the device over a broader range of operating conditions.As used herein, the term coating compound is intended to describe amaterial adapted to provide lubrication, anti-stiction, and/or anti-wearproperties to contact surfaces. The coating compound may generally be ina liquid, vapor and/or gaseous state during the operation and storage ofa MEMS device.

The presently described coating compounds differ from previous coatingsin that they comprise an amphiphilic molecule containing one or moreether functional groups interspersed in the carbon backbone of ahydrophobic tail section. In an embodiment shown in FIG. 1, anembodiment of an amphiphilic molecule 100 comprises a compound having ahydrophilic head group 104 (e.g., M) bound to a hydrophobic tail section102, and the hydrophobic tail section 102 comprises at least one etherfunctional group 106 (e.g., R—O—R′) disposed within the carbon chain ofthe hydrophobic tail. The hydrophobic tail section may comprise apartially or fully fluorinated carbon chain. Various compounds may beformed by modifying the particular placements of the ether group(s), bychanging the number of ether groups present in the hydrophobic tailsection, by changing the length and/or the branching of the hydrophobictail section, and/or by changing the composition of the hydrophilic headgroup. The particular number and configuration of the ether groups willmodify the performance and durability of any coating formed with theamphiphilic molecule.

In an embodiment, the coating may comprise a compound of one of theformulas:M(C_(n)(H,F)_(2n+1)O_(r))  (Formula I)M(C_(n)F_(2n+1)O_(r))  (Formula II)Formulas I and II represent partially (Formula I) and fully (Formula II)fluorinated (e.g., perfluorinated) coating compounds. In Formula I andII, M represents a polar head group that may generally be hydrophilic,(C_(n)(H,F)_(2n+1)O_(r)) represents a partially fluorinated hydrophobictail section, and (C_(n)F_(2n+1)O_(r)) represents a perfluorinatedhydrophobic tail section. The polar head group may comprise any polar orhydrophilic moiety configured to interact with a surface of a MEMSdevice or semiconductor device, such as through a chemisorptioninteraction. In an embodiment, M may comprise a central atom having acoordination number of 3, 4, or 5. A hydroxyl functional group may bebound to the central atom, and in some embodiments, the polar head groupmay comprise at least one oxygen atom. In an embodiment, the centralatom may be an oxygen atom. Various functional groups may be used toform the polar head group, and suitable functional groups may include,but are not limited to, a carboxylic acid functional group (e.g.,R—COOH), a sulfonic acid functional group (e.g., R—S(═O)₂—OH), aphosphonic acid functional group (e.g., R—P(═O)₂—OH), an amidefunctional group (e.g., R—CONH₂), a hydroxamide functional group (e.g.,R—CONHOH), or any combination thereof.

In Formula I and II, the subscripts n and r follow the relationship:n≧2r. In an embodiment, the number of carbon atoms in the hydrophobictail may range from 2 to about 20 carbon atoms (e.g., 2≦n≦20), oralternatively from about 4 to about 16 carbon atoms (e.g., 4≦n≦16). Thenumber of oxygen atoms present in the ether groups in the hydrophobictail section may range from 1 to 10 (e.g., 1≦r≦10). One or moreheteroatoms (e.g., O, N, S, etc.) may be present in the hydrophobic tailsection, and the total atom count in the backbone chain structure mayrange from 3 to about 30 atoms or alternatively from about 5 to about18. As an example, the total of n plus r may range from 3 to about 30,or alternatively from about 5 to about 18.

The hydrophobic tail section of the amphiphilic molecule may containone, two, three, or more ether groups interrupting the carbon chain. Inan embodiment with only a single ether group disposed within thehydrophobic tail section, the single ether group may be disposed at anyposition within the hydrophobic tail section so long as the carbon chainof the hydrophobic tail section begins and ends with a carbon atom. Forexample, the amphiphilic molecule may be represented by the formula:M-(CF₂)_(x)—O—(CF₂)_(y)—CF₃  (Formula III)In Formula III, the value of x may range from 1 to about 18, the valueof y may range from 0 to about 19, and the total of x and y may rangefrom 2 to about 19. While Formula III is shown as a perfluorinatedcompound, one or more of the fluorine atoms may be substituted withhydrogen to provide a partially fluorinated coating compound.

In an embodiment, a plurality of ether groups may be present in thehydrophobic tail section, and the oxygen atoms of the ether groups inthe hydrophobic tail section may be disposed at any positions within thetail section so long as they are separated by at least one carbon atom,and so long as the carbon chain of the hydrophobic tail section beginsand ends with a carbon atom. In an embodiment, the ether groups withinthe hydrophobic tail section may be separated by at least one carbonatom, and in an embodiment, the ether groups may be separated by six orfewer carbon atoms. Since an ether group includes a central oxygen atombound to two adjacent carbon atoms, the ratio of n:r in Formula I mayhave a minimum value of 2:1 and range as high as about 20:1, thoughhigher values may be possible.

Specific examples of the coating compound according to Formula I caninclude, among others, a perfluoropoly(alkylene) polyether carboxylicacid, a perfluoro(alkylene)polyether sulfonic acid, aperfluoro(alkylene) polyether phosphonic acid, aperfluoro(alkylene)polyether carboxamide, a perfluoro(alkylene)polyetherhydroxamide, or any combination thereof. The molecules of the coatingcompound may be approximately monodisperse, in that they can be formedfrom distinct, purified monomers or monodisperse oligomers. Suchmolecules can be classified as small-to-medium sized molecules ratherthan polymers. In an embodiment, the polydispersity of such lubricants(e.g., the polydispersity index) may be less than about 2.0, less thanabout 1.5, less than about 1.25, or about 1.0. In an embodiment, thepolydispersity may be as close to 1 as practically achievable throughnormal means of chemical synthesis and purification.

To illustrate the diversity of coating compounds that can be synthesizedand used with a MEMS or semiconductor component, a series of embodimentsis first described in which the polar head group is modified. As shownin FIG. 2, a first coating compound 202 comprisesperfluoro-3-oxadecanoic acid. In this embodiment, the polar head groupcomprises a carboxylic acid functional group, and the hydrophobic tailsection comprises C₈F₁₇O. Substitution of the polar head group whileleaving the hydrophobic tail section the same results in a variety ofcoating compound including: perfluoro-2-oxaoctane-sulfonic acid 204(e.g., having a polar head group comprising a sulfonic acid functionalgroup); perfluoro-2-oxaoctane-phosphonic acid 206 (e.g., having a polarhead group comprising a phosphonic acid functional group); andN-hydroxy-perfluoro-2-oxaoctanamide 208 (e.g., having a polar head groupcomprising an amide functional group).

As illustrated in FIG. 3, a series of embodiments is shown in which thecarbon chain length is modified while the placement of a single ethergroup within the tail section remains the same. The sequentialmodification starts with perfluoro-4-oxaheptanoic acid (COOH)—(C₅F₁₁O)302 having a carboxylic acid functional head group (COOH) and ahydrophobic tail section (C₅F₁₁O) comprising a single ether group. Withthe hydrophobic tail section, the ether group divides the carbon chainin the hydrophobic tail section into a first section having two carbonatoms and a second section having three carbon atoms. Sequentiallyadding additional carbon atoms to the tail section creates themolecules, perfluoro-4-oxaoctanoic acid (COOH)—(C₆F₁₃O) 304,perfluoro-4-oxanonanoic acid (COOH)—(C₇F₁₅O) 306, andperfluoro-4-oxadecanoic acid (COOH)—(C₈F₁₇O) 308, each having differentphysical properties and performances as coating compound for a MEMS orsemiconductor component.

As illustrated in FIG. 4, another series of embodiments is shown inwhich the number of carbon atoms in the coating compound molecule'sbackbone remains constant while changing the number of ether groupspresent. The sequential modification starts withperfluoro-3-oxaundecanoic acid (COOH)—(C₉F₁₉O) 402, having a carboxylicacid functional head group (COOH) and a hydrophobic tail section(C₉F₁₉O) comprising a single ether group located near the polar headgroup. Additional ether groups may be added to obtainperfluoro-3,6-dioxadodecanoic acid (COOH)—(C₉F₁₉O₂) 404,perfluoro-3,6,9-trioxatridecanoic acid (COOH)—(C₉F₁₉O₃) 406, andperfluoro-3,6,9,12-trioxatridecanoic acid (COOH)—(C₉F₁₉O₄) 408, eachhaving different physical properties and performances as coatingcompound for a MEMS or semiconductor component. For example, the coatingcompound may comprise perfluoro-3,6,9-trioxatridecanoic acid(COOH)—(C₉F₁₉O₃) (e.g., molecule 406 in FIG. 4). This molecule issimilar to a saturated perfluoro-compound perfluorodecanoic acid (PFDA)except for three ether (R—O—R′) functional groups that have beenintroduced into its carbon backbone at various intervals. Rather thanhaving a continuous sequence of ten carbon atoms as found in the PFDAbackbone, the coating compound has an overall backbone structure with aC—C—C—C—O—C—C—O—C—C—O—C—C atom sequence. Here, the molecule isamphiphilic, containing a polar head group (i.e., a carboxylic acidfunctional head group) and a perfluoroalkyl tail group. This molecule isfunctionally and chemically distinct from common perfluoropolyetherlubricants that contain polar functional groups at each end of themolecule.

The coating compound molecules may be synthesized using any suitablereaction route. For example, the coating compounds may be elaboratedfrom their hydrocarbon analogs by methods including direct fluorinationand functional group interconversion as taught, for example, by U.S.Pat. No. 5,753,776 to Bierschenk et al. which is incorporated herein byreference in its entirety. Suitable compounds may also be obtainedcommercially from suppliers such as Matrix Scientific of Columbia, S.C.and Synquest Laboratories of Alachua, Fla. Additional synthesis routesmay also be used as would be apparent to one of ordinary skill in theart with the aid of this disclosure.

The embodiments illustrated in FIGS. 2-4 are provided for illustration.Additional permutations consistent with the teachings of the presentdisclosure may provide additional compounds and molecules in addition tothose specifically illustrated and/or listed herein to create anycoating compound with the physical properties desired for a specificMEMS application.

As schematically illustrated in FIG. 5, the coating compounds 502described herein may be used to coat at least a portion of a surface 506of a MEMS or semiconductor component 504. In general, the coatingcompounds 502 may contact a surface 506 and interact with the surface506 to reduce the surface energy of the component 504 relative to anuncoated surface. In an embodiment, the coating compounds 502 may beconfigured to have a chemisorption interaction with the surface 506. Theinteraction of a coating compound 502 with the surface 506 may allow thecoating compound 502 to form a relatively thin coating on the surface506, which may comprise an ordered array of molecules, as described inmore detail herein. The coating compounds 502 described herein may beuseful with a MEMS or semiconductor component 504 having a functionalitycharacterized by intermittent surface-to-surface contact of mechanicalelements (e.g., such as in DMDs, microactuators, or devices withsimilarly relatively movable elements), a continuous surface-to-surfacesliding contact of mechanical elements (e.g., in a micromotor,microactuator, or similarly operating device), a functionality derivedthrough the controlled surface energy of the surfaces on elements (e.g.,such as in a sensor or equivalent device), a functionality derivedthrough the protection or passivation of the surfaces on elements (e.g.,such as in a sensor or equivalent device), and/or a functionalityderived through the dielectric properties of the surfaces on elements(e.g., such as in a variable capacitor, microswitch, or equivalentdevice). The coating compounds 502 may also be useful in othersituations where a modified surface is part of any device or machinethat benefits from having functional surfaces coated with a hydrophobicpassivant or lubricant. Suitable MEMS and/or semiconductor components504 may include, but are not limited to, radio frequency (RF) switches,optical modulators (e.g., SLMs), microgears, accelerometers, worm gears,transducers, fluid nozzles, gyroscopes, and other similar devices oractuators.

In an embodiment, a MEMS device may comprise a digital micromirrordevice (DMD) such as a Texas Instruments DLP™ micromirror device. TheDMD generally comprises a mirror/yoke assembly configured to rotate on atorsion hinge until the yoke tips contact (land on) landing pads. Insome cases the mirror/yoke assemblies become slow in lifting off thelanding pad, affecting the response of the device and in other cases theassemblies become permanently stuck to the landing pads. One of theprimary causes of stiction has been shown to be that of the landing tipsscrubbing into the metal landing pads. The stiction problem may beaddressed by coating or passivating the metal surfaces of the deviceswith any of the coating compounds described herein. The coatingcompound(s) may tend to decrease the van der Waals forces associatedwith the mirror assemblies in the DMD or any moving parts in a MEMSdevice, and thereby reduce the tendency for the mirrors to stick to thelanding pads.

In an embodiment, a MEMS and/or semiconductor component may beincorporated into a larger assembly or package. The coating compound maybe disposed over a portion of the MEMS and/or semiconductor componentprior to the component being disposed in the package, or the package,including the MEMS and/or semiconductor component, may be coated withthe coating compound prior to being sealed. Such packages may retain thecoating compound, protect against contaminants such as dust, moisture,and the like, and generally protect the MEMS and/or semiconductorcomponent.

In an embodiment, a DMD may be incorporated into a device package. Thepackage may comprise a frame and a lid such as cover glass. The coverglass can be made opaque on the underside with a transparent aperturefor optical interfacing with the device. As mentioned, this stictionproblem has normally been addressed by attempting to control theenvironment inside the packages. For example, the coating compound canbe disposed on the DMD within the package and then sealed to retain thecoating compound within the package. As discussed in more detail herein,the coating compound may exist as a thin layer of liquid in equilibriumwith a vapor. The package may then act to contain not only the MEMSand/or semiconductor device, but also to retain the coating compoundwithin the package. The coating compound may be in a solid or liquidstate, depending on the properties of the material, and the temperatureand pressure or environment in which the coating compound is placed. Ingeneral, the terms a “solid” or a “liquid” coating compound refers to acompound that is in a solid or liquid state under ambient conditions,i.e., room temperature and atmospheric pressure. The term “vapor” phasecoating compound generally describes a mixture of components thatcontain a carrier gas (e.g., nitrogen) and a vaporized component that isa solid or liquid at temperatures and pressures near ambient conditions(e.g., STP).

Whether formed on a portion of a surface of a MEMS and/or semiconductorcomponent, over an entire surface, and/or contained within a largerpackage, the coating compound may form a thin layer on the MEMS and/orsemiconductor component. In an embodiment, a MEMS and/or semiconductorcomponent may be received (e.g., step 602 of FIG. 6) and a coating maybe disposed on a surface of the component (e.g., step 604 of FIG. 6).The coating compound may be capable of forming a monolayer orself-assembled monolayers (SAMs) at the device surface based on theamphiphilic nature of the compounds (e.g., Step 606 of FIG. 6). In orderto form a monolayer or SAM, the coating compound may be exposed to thesurface and the hydrophilic head group of the molecule may bond/interactto the MEMS and/or semiconductor surface in an orientation that pointsits hydrophobic tail section away from the surface. Van der Waals anddispersion forces can cause the tails to adopt a closely packedorientation upon a sufficient molecular density on the surface. For somecoating compounds, substantially all of the molecules may align this wayto give a nearly crystalline order. Some molecules may interact withother molecules rather than the surface. Still further, the compositionof the hydrophobic tail section may affect the packing efficiency of themonolayer. The misalignments and secondary molecular interactions maycreate an imperfect, SAM-like coating on the surface of the MEMS and/orsemiconductor component surface. As used herein, the term monolayer mayrefer to a SAM, a SAM-like layer, or other monolayer.

Once the MEMS surfaces are coated with a sufficiently dense andorganized SAM or SAM-like layer, the surface energies can be reduced,and the incidence of adherence may be reduced or eliminated (e.g., Step608 of FIG. 6). Increasing fluorination of the hydrophobic tail sectioncan provide for a lower surface energy performance. The use of the ethergroups in the hydrophobic tail section of the coating compoundsdescribed herein may limit the degree of self-assembly achievable withthe coating compound described herein.

Any suitable method for depositing a thin film layer or a coating on asurface of a MEMS or semiconductor component may be used. Suitablemethods may include, but are not limited to, an evaporative depositionprocess, a spin-on or spray on process, or any other suitabletechniques. In evaporative deposition, evaporated material condenses ona substrate to form a layer. In spin-on, spray-on, or dip-on deposition,a coating material is applied, typically from a solvent solution of thecoating material, and the solvent is subsequently evaporated to leavethe coating material on the substrate.

In any of the application processes, the surface of the MEMS and/orsemiconductor component should be exposed to the coating compound for atime sufficient for a coating or layer (e.g., a monolayer) to form. Thetime may be in the range of minutes to hours. The resulting thin filmmay vary in thickness from about 3 angstroms (Å) to about 1,000 Å. Forany process, monolayer formation can be verified by measuring liquidcontact angles on a test surface. Once the coating has been applied, theMEMS and/or semiconductor component may be enclosed and/or sealed withina package or larger container (e.g., step 608 of FIG. 6).

The disposition of the coating compound on the surface of the MEMScomponent and/or semiconductor component may result in a thin layer ofmaterial that can damaged or displaced due to impact or wear created bythe interaction of the various moving components. Such contact may occurin MEMS and/or semiconductor components with contacting surfaces thatare subject to frequent contact in use and a large number of contactsduring the product lifetime, such as in optical modulators (e.g., a SLM,an RF switch, etc.). In an embodiment, the particular coating compoundor combination of coating compounds may be selected so that a portion ofthe coating compound vaporizes to form a vapor or gas within theprocessing region during normal operation of the device. The ability ofthe coating compound to form a vapor or gas is dependent on coatingcompound equilibrium partial pressure, which varies as a function of thetemperature (e.g., expected operating temperature range) of the coatingcompound, the pressure of the region surrounding the coating compound,the coating compound bond strength to internal surfaces of theprocessing region, and the coating compound molecular weight. In anotherembodiment, the coating compound may be selected based, at least inpart, on its ability to diffuse along a surface of the MEMS and/orsemiconductor component within the processing region. In thisembodiment, one or more surfaces of the MEMS and/or semiconductorcomponent, or package in which the component is contained, may betreated to act as wetting surfaces for the coating compound. In thisway, coating compound may be mobile to allow replacement coatingcompound to flow into any damaged layer of the coating compound.

In terms of the coating compounds described herein, the selection of thenumber of ether groups present in the hydrophobic tail section may bebased, at least in part, on considerations such as the resultingmolecular weight of the coating compound and the melting point and/orvapor pressure of the coating compound over the expected operatingrange. In an embodiment, the ether groups within the coating compoundmay allow the MEMS and/or semiconductor component to operate at atemperature that is within an extended operating temperature range. Forexample, the coating compound may be configured to allow a MEMS and/orsemiconductor component to operate at a temperature ranging from about−50° C. to about 150° C., or about 0° C. to about 100° C.

It should be understood that the MEMS and/or semiconductor devicesdescribed herein are not intended in any way to limit the scope of theinvention described herein, since one skilled in the art wouldappreciate that the various embodiments described herein could be usedin other MEMS, NEMS, larger scale actuators or sensors, or othercomparable devices that experience stiction or other similar problems.

EXAMPLES

The disclosure having been generally described, the following examplesare given as particular embodiments of the disclosure and to demonstratethe practice and advantages thereof. It is understood that the examplesare given by way of illustration and are not intended to limit thespecification or the claims in any manner.

Example 1 Lubrication of a Standard XGA DMD

In a first example, a MEMS component comprising a DMD was coated with acoating compound as described herein. Immediately after micromirrors ofa DMD were released from their underlying silicon substrate,perfluoro-4-oxadecanoic acid was applied from the vapor phase to coatall exposed surfaces of the DMD with a SAM. At this point in the DMD'smanufacturing sequence, the perfluoro-4-oxadecanoic acid did not act asa lubricant but rather as a passivant film, protecting the MEMS elementsfrom attack by ambient moisture until additional intermediate processingon the device could be completed. Just prior to sealing the DMD with alid, the device was again exposed to vacuum and a new coating ofperfluoro-4-oxadecanoic acid applied, again from the vapor phase. Afterthe completion of all assembly processes, the DMD was tested undervarious environmental conditions of light, heat, and moisture toevaluate the mechanical performance of its micromirrors. It was observedthat relative to PFDA, perfluoro-4-oxadecanoic acid was about 10% lesseffective as a lubricant and that a slightly additional amount of motiveforce was required to toggle the micromirrors between their ON and OFFstates. However, this coating compound was found to be more resistant tomoisture degradation, allowing for higher levels of moisture to bepresent within the package. Additional DMD devices of this typecontaining the perfluoro-4-oxadecanoic acid coating compound were testedand were found to operate nominally when installed in typical businessor consumer grade digital projector products.

Example 2 Lubrication of a High-Lumens XGA DMD

In a second example, another MEMS component comprising a DMD was coatedwith a coating compound as described herein. The DMD device tested wasrepresentative of DMD devices installed in digital projectors that havehigher than typical operating temperatures and light load. Previoustesting found that perfluoro-4-oxadecanoic acid was a less reliablelubricant under these conditions. Engineering evaluations found thatperfluoro-3,6,9-trioxatridecanoic acid with a C₄ carbon tail was asuitable drop-in replacement for perfluoro-4-oxadecanoic acid, and DMDscontaining this coating compound were assembled using the manufacturingsequence described in Example 1, above. After the completion of allassembly processes, these DMDs were tested under various environmentalconditions of light, heat, and moisture to evaluate the mechanicalperformance of their micromirrors. It was observed that relative toPFDA, perfluoro-3,6,9-trioxatridecanoic acid was about 15% lesseffective as a coating compound and that a slightly additional amount ofmotive force was required to toggle the micromirrors between their ONand OFF states. However, this coating compound was more resistant tophotochemical and thermal degradation present in this type ofapplication.

Example 3 WVGA DMD with Improved Cold Start Capability

In a third example, another MEMS component comprising a DMD was coatedwith a coating compound as described herein. The DMD device tested wasrepresentative of DMD devices installed in digital projector systemsthat are deployed in sub-freezing temperature environments. Engineeringevaluations found that perfluoro-3,6,9-trioxatridecanoic acid was asuitable lubricant under these conditions, and DMDs containing thiscoating compound were then assembled using the manufacturing sequencedescribed in Example 1, above. After the completion of all assemblyprocesses, these DMDs were tested under sub-freezing temperatureenvironmental conditions to evaluate the mechanical performance of theirmicromirrors. It was observed that relative to PFDA,perfluoro-3,6,9-trioxatridecanoic acid extended the cold operating limitof the devices by several tens of Celsius degrees lower than possiblewith the use of PFDA.

At least one embodiment is disclosed and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of the disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of the disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R_(l), and an upperlimit, R_(u), is disclosed, any number falling within the range isspecifically disclosed. In particular, the following numbers within therange are specifically disclosed: R=R_(l)+k*(R_(u)−R_(l)), wherein k isa variable ranging from 1 percent to 100 percent with a 1 percentincrement, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5percent, . . . , 50 percent, 51 percent, 52 percent, . . . , 95 percent,96 percent, 97 percent, 98 percent, 99 percent, or 100 percent.Moreover, any numerical range defined by two R numbers as defined in theabove is also specifically disclosed. Use of the term “optionally” withrespect to any element of a claim means that the element is required, oralternatively, the element is not required, both alternatives beingwithin the scope of the claim. Use of broader terms such as comprises,includes, and having should be understood to provide support fornarrower terms such as consisting of, consisting essentially of, andcomprised substantially of. Accordingly, the scope of protection is notlimited by the description set out above but is defined by the claimsthat follow, that scope including all equivalents of the subject matterof the claims. Each and every claim is incorporated as furtherdisclosure into the specification and the claims are embodiment(s) ofthe present invention.

The invention claimed is:
 1. A method of fabricating amicroelectromechanical system (MEMS) device comprising: forming a MEMScomponent having a surface; and coating at least a portion of thesurface with a compound of the formula M(C_(n)F_(2n+1)O_(r)), wherein Mcomprises a polar head group, and wherein n≧2r.
 2. The method of claim1, wherein the polar head group comprises a central atom having acoordination number of 3, 4, or
 5. 3. The method of claim 2, wherein thepolar head group comprises an oxygen atom bound to the central atom. 4.The method of claim 3, wherein the polar head group comprises a hydroxylfunctional group bound to the central atom.
 5. The method of claim 1,wherein the polar head group comprises at least one functional groupselected from the group consisting of: a carboxylic acid functionalgroup; a sulfonic acid functional group, a phosphonic acid functionalgroup, an amide functional group, and a hydroxamide functional group. 6.The method of claim 1, wherein n has a value ranging from 2 to about 20.7. The method of claim 1, wherein r has a value ranging from 1 to about10.
 8. The method of claim 1, wherein n+r ranges from 3 to about
 30. 9.The method of claim 1, wherein a ratio of n:r has a value of about 2:1to about 20:1.
 10. The method of claim 1, wherein the MEMS componentcomprises a digital micromirror device.
 11. The method of claim 1,wherein the MEMS component comprises at least one of an actuator, amotor, an RF switch, a sensor, a variable capacitor, an opticalmodulator, a microgear, an accelerometer, a transducer, a fluid nozzle,a gyroscope, or any combination thereof.
 12. The method of claim 1,wherein the compound is coated on the at least the portion of thesurface as a self-assembling monolayer.
 13. The method of claim 1,wherein a polydispersity of the compound is less than about 2.0.
 14. Themethod of claim 1, wherein the compound comprises at least one materialselected from the group consisting of: a perfluoropoly(alkylene)monoether carboxylic acid, a perfluoro(alkylene) monoether sulfonicacid, a perfluoro(alkylene) monoether phosphonic acid, aperfluoro(alkylene) monoether carboxamide, and a perfluoro(alkylene)monoether hydroxamide, a perfluoropoly(alkylene) polyether carboxylicacid, a perfluoro(alkylene)polyether sulfonic acid, aperfluoro(alkylene)polyether phosphonic acid, aperfluoro(alkylene)polyether carboxamide, and aperfluoro(alkylene)polyether hydroxamide.
 15. The method of claim 1,wherein the compound comprises at least one material selected from thegroup consisting of: perfluoro-3-oxadecanoic acid,perfluoro-2-oxaoctane-sulfonic acid, perfluoro-2-oxaoctane-phosphonicacid, N-hydroxy-perfluoro-2-oxaoctanamide, perfluoro-4-oxaheptanoicacid, perfluoro-4-oxaoctanoic acid, perfluoro-4-oxanonanoic acid,perfluoro-4-oxadecanoic acid, perfluoro-3-oxaundecanoic acid,perfluoro-3,6-dioxadodecanoic acid, perfluoro-3,6,9-trioxatridecanoicacid, and perfluoro-3,6,9,12-tetraoxatetrdecanoic acid.